The present disclosure generally relates to apparatuses for chemical mechanical planarization and methods for operating the same.
As semiconductor technologies and methods have advanced over time, chemical mechanical planarization (CMP) processes and tooling have been modified for the purpose of controlling many required aspects of the CMP processes and the end result thereof. A few exemplary aspects interrelated through the CMP processing include, but are not limited to, within-wafer non-uniformity, ultralow dielectric constant films and the associated sensitivities to process forces and induced stresses, extremely fine pattern dimensions and the associated sensitivities to defects and material loss from within patterned features, and increasing sizes of the substrates, e.g., from 125 mm, to 200 mm, to 300 mm, and then to a proposed 450 mm in the diameter of a substrate.
There have been many attempts at novel CMP apparatus and methods towards addressing such aspects of the CMP. With respect to novel CMP Polish Platforms, while these all had their own individual strengths or focuses, they also lacked overcoming one or more of the fundamental issues associated with the historical and currently used rotational platform and, thus, failed in the end. With regard to the rotational CMP platform widely recognized and used in the industry as the CMP standard, the CMP module has evolved into a system that makes use of very complex mechanical apparatus and process control schemes in an attempt to combat these fundamental issues.
One such example is the industry wide acceptance of the pressurized wafer carrier. This wafer carrier is divided into several ‘zones’ each with its own ‘air bladder’ for the purpose of controlling within-wafer non-uniformity by applying varying forces radially across the backside of the wafer during the polish cycle. For the bladder pressures required to adequately compensate for within-wafer non-uniformity, it was found the wafer would slip out during the course of the polish cycle. The ‘retaining ring’ forms the ‘pocket’ that retains or holds the wafer in place during the course of polishing. Historically, the retaining ring did not contact the surface of the polishing pad, but rather was mounted to the carrier with a fixed depth to the pocket that allowed ˜0.008″-0.012″ of wafer protrusion. With the potential for wafer slip, this bladder carrier also required a design change to incorporate a pressurized retaining ring such that said retaining ring is in contact with the polishing pad surface to better hold the wafer during the polish cycle.
Another aspect of within-wafer non-uniformity is a very local region referred to as the ‘edge bead’ or 1-5 mm region at the perimeter of the wafer. Typically, the polish removal at this region is significantly different than the remainder or ‘body’ of the wafer due to the compression of the pad material as it meets the bevel of the wafer during rotation on the leading edge of the wafer carrier and the subsequent relaxation of the pad material at it is drawn across the surface wafer. Historically, only the wafer and pad contact created this edge bead issue. With the advent of the pressurized retaining ring, there are now two regions of contact that require controlling to reduce the edge bead impact—the retaining ring itself, as well as the bevel of the wafer now tucked inside the width of this retaining ring. The pressurized retaining ring can be a benefit to reducing the historical edge bead effect. However, it has been found—as the pressure applied to the retaining ring is coupled to the pressures applied to the zones of the bladder carrier—this additional mechanical component can also amplify the problem at the edge region of the wafer. In addition, fluid dynamics have always been a complicated component of the rotational platform. Adequate fresh slurry distribution across the entire wafer and removal of spent effluent in an efficient manner are both known to contribute to within-wafer non-uniformity and defectivity levels. The introduction of a retaining ring that rides in contact with the surface of pad has served to further inhibit the flow of fluids.
While the design and capabilities of the bladder carrier as known in the art provides some benefits, one must also accept the accompanying added complexity to the design, the maintenance, and ultimately the CMP process itself caused by use of the bladder carrier.